def fac(k):
    i = 2
    t = 1
    while i <= k:
        t *= i
        i += 1
    return t
def sum(n):
    s = 0
    i = 1
    while i <= n:
        s = s + fac(i)
        i += 3
    return s
print('1!+4!+7!...50!=', sum(50))
